Problem: $ C = \left[\begin{array}{rrr}1 & 1 & 2 \\ 2 & 2 & 2 \\ 1 & 2 & 0\end{array}\right]$ What is $ C^{-1}$ ?
Answer: $ = \left[\begin{array}{rrr}-2 & 2 & -1 \\ 1 & -1 & 1 \\ 1 & -\frac{1}{2} & 0\end{array}\right]$